The present invention relates to a numerical control apparatus for controlling an operation of a machine tool.
Typical examples of a conventional numerical control (NC) apparatus are shown in FIGS. 5 and 6. In FIG. 5, control objects to be controlled by a single control instruction are an axis control and two MST controls and, in FIG. 6, control objects to be controlled by two control instructions are two axis controls and two MST controls.
In FIG. 5, 1a depicts the control instruction for the control objects 2, 3 a numerical control apparatus responsive to the control instruction for controlling the control objects, 4 an instruction decoder, 5 an axis control circuit responsive to a portion of the instruction concerning movement of an axis for controlling movement of the axis, 6 an auxiliary instruction control circuit for controlling an auxiliary instruction M, a main spindle instruction S and a tool instruction T, etc., 7a a control object to be axis controlled by the axis control circuit and 8a and 8b independently movable objects to be controlled by the auxiliary instruction control circuit.
Each control instruction i for controlling objects is prepared as a machining program and is decoded block by block by the instruction decoder circuit 4 to perform a numerical computation so that data of the axis control instruction and auxiliary instructions (MST instructions) which have no relation to the axis control are obtained. In the axis control circuit 5, an interpolation and pulse distribution are performed on the basis of respective axis movement data, speed data and data of the kind of interpolation among instruction data of the axis control to drive a servo motor through a drive amplifier to thereby control the axis control objects 7a. The auxiliary instruction data are processed individually in the auxiliary instruction control circuit 6 on tha basis of the data of the M instruction, the S instruction and the T instruction and control the auxiliary instruction control objects (8a) and (8b) through mechanical input/output interface. It should be noted that, only after the axis control and the auxiliary instruction control of a block are completed, a control of a subsequent block can be done.
FIG. 7 is a time chart showing this control. In FIG. 7, M10, M11 and M12 of the auxiliary instruction 1 and M21 and M22 of the auxiliary instruction 2 can be executed individually. However, when they are instructed in the same block, a next block can not be executed unless the auxiliary instructions 1 and 2 are completed. Therefore, an execution of a block N3 can not be done unless the M11 instruction completes even if the M21 instruction is completed.
In FIG. 6 in which components depicted by same reference numerals as those used in FIG. 5 are identical to the components in FIG. 5, respectively, a numerical control apparatus 3 includes a pair of control portions 3a and 3b which are responsive to mutually independent control instructions 1a and 1b, respectively. Each control portion comprises an instruction decoder circuit 4, an axis control circuit 5 and an auxiliary instruction control circuit 6, which are identical to those components 4, 5 and 6 of the numerical control apparatus 3 shown in FIG. 5 and operate similarly. The control portion 3a controls an axis control object 7a and an auxiliary instruction control object 8a and the control portion 3b controls an axis control object 7b and an auxiliary instruction control object 8b. In this construction, two pairs of the axis and the auxiliary instruction can be controlled separately. However, the control portion 3b can not control the auxiliary instruction alone. When it is desired to operate either of the control portion, it is necessary to modify it such that it functions like the apparatus shown in FIG. 5.
In either the apparatus shown in FIG. 5 or that shown in FIG. 6, it is impossible to control two or more auxiliary instructions independently from others, resulting in an increase of execution time. Such control may be possible in an apparatus having two or more control portions, only when there is an object to be axis-controlled. Further, when it is desired to add an object which is to be controlled independently from others, it is necessary to modify the construction of the control apparatus itself completely. This means that a flexibility of the control apparatus for change of the control object is very low.